lektor January & February 2021 7The chosen BQ24092 comes from a BQ2409x line and this is where
you need to check the datasheet carefully. Depending on the chip
chosen the mentioned resistor needs to be 10 k or 100 k, and it was
easier to change the resistor than the whole charger IC. There are more
lessons learned as we did three iterations. How to fix the disintegrat-
ing DC/DC converter is something that is quite simple if you know
what parts you can choose. Also some do’s and don’ts were made
during the iterations and for manufacturing we may have also a few
lessons learned you can benefit from. Meanwhile you can check out
the Youtube channel of GreatScott! and see the assembly and the
power supply in action. Details and an in-depth description of the
circuitry will follow next time. The rough specifications are presented
in the nearby textbox. The final revision of the PCB looks like what
you see in Figure 3. Figure 4 shows it in action..
191188-The three ICs that make the board work are from a well-known vendor.
The battery protection IC is a XB8089D from Xysemi, a chip only
found at distributors that specialize in Chinese silicon products. This
chip handles overcharge , over discharge, over current and reverse
polarity protection in a small SOP8 package with expose pad for a
reasonable price. While many batteries used in products like drones
have integrated protection, it won’t be safe to remove the chip from
the circuit if a lithium battery without protection is installed.
With the sketches and rough schematic GreatScott provided, Elektor
added their experience in creating and designing PCBs. You might
think this is the end of the story (you have a PCB and everything is
fine), but as rule of thumb, it usually takes three iterations, as you can
see at Figure 2. The first prototype worked almost as expected besides
a few minor issues, like not charging the battery or disintegrating the
DC/DC converter if load exceeded a certain point. The battery protec-
tion IC will prevent the lithium battery form becoming damaged ( sort
of ) but the current limit is at 10 A ( meaning 37 W ), so the DC/DC
converter disintegrated at around 15W. And the charging, that was
an easy fix, as there was somewhere a typo, making the desired 10 k
resistor a 100k resistor, it was just a short swap of components. But
to be honest, we know where to look when it comes to the wrong
resistor for charging as we have seen this in other projects before.
Figure 2: The three iterations from left to right.
Figure 4: PCB in action.Figure 3: Assembled PCB.[1] GreatScott! Youtube channel: http://www.youtube.com/c/greatscottlab/
[2] GreatScott interview: http://www.elektormagazine.com/news/elektor-magazine-2020-summer-editionWEB LINKSSPECIFICATIONS
Input: 5 V +/– 10%
Output: 5 V / 1.5 A or 12 V /0.75 A
Single Cell Lithium battery